I have a 2012 R2 VM with a newly provisioned secondary virtual HDD, on a new VM datastore that sits on a new nimble volume.

Secondary Virtual HDD - 100GB

VM - Datastore 125GB

Nimble Volume - 125GB

Onto the question/issue

On the 2012 R2 box I loaded up the new HDD with 4.2GB of data, watched the usage grow inside of the nimble reporting then sometime after I peramnently deleted the data from within the Guest OS. I waited a few days, but the usage on the Nimble Volume was still showing 4.2GB. So the data was permanently deleted from the 2012 R2 VM, but the Nimble Volume is still showing that 4.2GB as usage. Is this a VMware issue or a Nimble issue? Do I have to look at the VMware Datastore for releasing these blocks?

Environment - ESXi 6.0 latest Update, 2012R2 Guest OS, Nimble CS300 w/ latest FW. So the data was permanently deleted from the 2012 R2 VM, but the Nimble Volume is still showing that 4.2GB as usage. Is this a VMware issue or a Nimble issue? Do I have to look at the VMware Datastore for releasing these blocks?

If you'd like the VM to shrink is size you'd need to do a storage vmotion, if you'd like the VMFS datastore to free up deleted space to the nimble you'd need to issue a unmap command

VMFS 5 Cleanup -

esxcli storage vmfs unmap -l exact-datastore-name-here

Also, there's some great documentation on InfoSight for a better understanding

My understanding is that only works if your virtual hdd's are allocated using thin provisioning from the datastore they're using. Mine use thick, so in VMware despite what data is on the GuestOS it reports 100GB of 125GB "in use" under the datastore in VMware. While Nimble shows 0GB of 125GB in use.